Automatic dishwashing detergents for use in domestic dishwashing appliances need to be able to effectively remove stains of foods and beverages, especially tea and coffee, from household dishware. Heretofore, alkaline products containing chlorine bleach have typically been used for this purpose. Many such products also use high (20% or more) levels of phosphate builders. It is desirable, however, to replace such chlorine bleach-reliant automatic dishwashing product systems with effective alternatives. Reasons include: minimizing the aggressive effect of chlorine bleach and alkalis on valuable consumer items such as silverware, china and crystal; increasing the compatibility of bleach ingredients with other excellent cleaning agents, particularly enzymes; maximizing product safety; and complying with regulatory requirements in different geographies.
Oxygen bleach, specifically perborate in combination with the bleach activator tetraacetylethylenediamine (TAED), has been introduced commercially as a chlorine bleach replacement in certain automatic dishwashing products. However, testing demonstrates that, with or without the TAED component, this bleach system is very poor in its effectiveness, even when used at much higher levels than a chlorine system, on a mass basis.
Persulfates have also been proposed as an alternative bleach. A number of persulfates exist, including potassium peroxydisulfate and monopersulfate salts. The latter, in general, are salts derived from Caro's acid or monopersulfuric acid, H.sub.2 SO.sub.5. Monopersulfate salts, such as the potassium, sodium, and magnesium salts, as well as binary and ternary mixed salts of monopersulfate with alkali metal sulfates and/or bisulfates, are generally known from the literature. One such salt, sold commercially as OXONE.RTM. (registered trademark of DuPont), has been variously described as a mixture of potassium monopersulfate with potassium sulfate and potassium bisulfate, or as a "triple salt" having specific stoichiometry.
Monopersulfate salts are chemically different from peroxydisulfate salts, such as potassium peroxydisulfate, K.sub.2 S.sub.2 O.sub.8. Indeed, peroxydisulfate alone is not effective in the instant invention. Despite some success in denture cleaners, monopersulfate bleach has not been commercially successful in dishwashing detergents any more than has peroxydisulfate. Yet it would be very desirable to use a persulfate bleach in automatic dishwashing, on account of good redox properties and the environmental acceptability (no chlorine, phosphorus, or boron) of persulfate decomposition products (e.g., sulfate, oxygen).
Possible reasons for the lack of widespread use of persulfate in automatic dishwashing include: lack of mass efficiency, particularly for the OXONE form; and slow action (kinetics) under automatic dishwashing conditions as compared with chlorine bleach. Nonetheless, some progress has been made in formulating OXONE in automatic dishwashing detergents. See commonly assigned WO 93/18129 as well as the documents included in the section entitled "Background Art".
A number of systems have been described in the art for promoting more effective bleaching, especially by perborate or percarbonate salts. For example, various efforts have been made to improve the efficacy of bleach activators and hundreds of such activators have been described. Reasons for the lack of commercially successful improvements may include an emphasis on laundry improvements not easily adaptable for automatic dishwashing. Bleach activators may, for example, yield unacceptably depositing, foam-forming or malodorous peracids, none of which are acceptable for automatic dishwashing, especially in a spray-action domestic dishwasher. There has been little teaching in the art as to which of the now so numerous bleach activators would be problem-free, and at the same time more effective than TAED, in the unique automatic dishwashing context.
The disclosure of many bleach activators in the context of laundry formulations includes the suggestion that quaternary-substituted versions of such activators may be of a depositing nature and have desirable fabric conditioning properties. See, for example, U.S. Pat. No. 4,751,015 at col. 3, lines 22-27. In light of this teaching and in view of the conventionally recognized need to minimize deposition tendencies of ingredients in automatic dishwashing, the automatic dishwashing detergent formulator would be inclined to avoid such bleach activators. This patent as well as U.S. Pat. Nos. 4,904,406 and 4,818,426 are illustrative of disclosures of bleach activators which may include chemical groups which may be cationic and/or which may form peroxy-carbonic acids when perhydrolyzed.
Metal-containing bleaching action "accelerators" or catalysts have also been described in the literature. Thus, automatic dishwashing detergents containing oxygen bleach with a manganese catalyst are known. See U.S. Pat. No. 5,246,612. Typically, such systems use a combination of manganese catalyst with sodium perborate, optionally with a bleach activator such as TAED. See the examples of '612.
Further, U.S. Pat. No. 5,246,612 recites, under the heading "peroxygen compound", a list of "hydrogen peroxide sources". Perborates, percarbonates, perphosphates and persulfates (without specifying whether monopersulfates, dipersulfates or both are intended) are included in this list. It is, in fact, technically incorrect to term a monopersulfate a "hydrogen peroxide source": under common detergency conditions, monopersulfate salts are not a source of hydrogen peroxide. There is no indication in '612 that any specific mixture of persulfates and perborates should be used in combination with catalyst or any of certain specific bleach activators disclosed hereinafter.
All the foregoing developments notwithstanding, there is an ongoing need for improved oxygen bleach detergents, especially automatic dishwashing detergents. In short, bleach activators tend to be expensive and may not be compatible with automatic dishwashing while persulfates, perborate and percarbonate all are slow-acting or ineffective, even when combined with common bleach activators. Moreover, transition-metal bleach catalysts may in some circumstances decompose and leave residues on dishware, thus, even the "bleach catalyst" approach is not without its limitations.
Accordingly it is an object herein to provide an improved oxygen bleach detergent, especially an automatic dishwashing detergent or a soak-type tea-pot cleaner, having an effective multicomponent oxygen bleach system which overcomes one or more of the disadvantages of the art-taught combinations of oxygen bleach ingredients.
It has now surprisingly been discovered that efficient and economical compositions for removal of beverage stains such as tea and coffee from substrates including, but not limited to, ceramics, porcelain and the like are secured from a particular combination of monopersulfate bleach and hydrogen peroxide-releasing bleach at specific ratios, provided that there is also present a cationic bleach activator. Most generally, the cationic bleach activator includes any of the known cationically charged (typically, quaternary nitrogen-containing) bleach activators hitherto recognized for use in combination with sodium perborate. Any of the cationic bleach activators identified hereinafter can be useful herein.
The present invention has multiple advantages, including making monopersulfate more useful, especially at reduced levels, to the automatic dishwashing detergent formulator; rendering the use of chlorine bleach unneccessary; improving tea stain removal over that attainable using perborate/TAED; and providing for the consumer dishwashing detergents having an excellent overall combination of tea stain removal, dishcare, and cleaning. The compositions are more enzyme-compatible than those hitherto formulated with monopersulfate.